Dielectric composition



Oct. 29, 1935. v C M, 2,019,338

DIELECTRIC COMPOSITION Filed Jan. 16, 1934 HALOGEN/7E0 OLEfl/V 40 I00 FERCENMGIS 0F CONST/TUENTJ HALOGENATED OLEF/N AND HALOGE/VATED D/Pf/E/YYL Inventor: Frank M. Clark I by His A'EtoYney.

Patented Oct. 29, 1935 UNITED STATES- DIELECTRIC COMPOSITION Frank M, can, Pittsiield, Mass, aasignor to General Electric Company, a corporation of New York Application January 16. 1934, Serial No. 706.852 8 Claims. (Cl. 252-1) The present invention relates to halogenated organic compositions comprising wholly or in part unsaturated compounds of the olefin type, such compositions being suitable for use as dielec- 5 tric materials in electrical devices, such as transformers, capacitors, switches, and the like.

As described in my prior United States Patents 1,931,373 and 1,931,455, both issued October 17, 1933, it is advantageous to employ in electrical devices a dielectric material comprising one or more liquid halogenated hydrocarbons containing a sumciently high proportion of halogen to insure non-inflammability of suchgases .as might be evolved by decomposition of a dielectric by an are or otherwise. Heretofore only halogenated aromatic h drocarbons have proved to be willciently stable for this purpose.

Q I have discovered that the chemical instability heretofore experienced with dielectric materials 0 comprising aliphatic halogenated compounds is associated with the chemical saturation of the carbon atom to which the halogen is chemically attached, or, in other words, that chemically saturated carbonatoms possess an electronic con-- carbon atom of halogenated benzene compounds characterized by similar chemical stability.

to Aliphatic compounds which I have found to possess unlocked-for chemical stability are the halogenated derivatives of the olefins, such, for example, as the chlorinated ethylenes or propylenes containing the chlorine atom or atoms atl5 tached to the unsaturated carbon or carbons, andv also cyclic or aromatic derivatives of such compounds with or without halogen substituted in the aromatic nucleus in addition to the halogen on the olefinic carbons. The introduction of the i0 aromatic group does not aflect the chemical sta- .,bility of the chlorine atoms chemically united to the unsaturated carbons. Chlorinated styrolene .and chlorinated divinyl benzene containing the chlorine atoms either attached to the un- 55 saturated carbons of the aromatic group 'or the olefin group are further illustrations of chemically stable halogenated olefin derivatives. If a material is desired which not only is noninfla mmable in itself but which under decomposition for any reason sh'all evolve only non-inflammable gases, 5 it is necessary to introduce suflicient halogen into the molecule that it contains an amount of halogen at least chemically equivalent to the amount of hydrogen present.

Dielectric compositions included in the present 10 invention also comprise mixtures of one or more halogenated oleilns and one or more halogenated aromatic hydrocarbons, such, for example, as mixtures of a chlorinated olefin and chlorinated diphenyl or chlorinated benzene, or both.

The accompanying drawing shows in Fig. l

in side elevation and partly 'in section a-transformer containing a. halogenated olefin dielectric composition and Fig. 2 is a graph showing the depression of point or congealing temperature resuiting when a halogenated cyclic compound is mixed with a halogenated olefin.

The term "olefin" has been used herein to describe the compounds of a class which I have foundto possess chemical stability, including both (1) the aliphatic compounds having the general formula Cpl-12a containing unsaturated carbons and (2) substituted aliphatic compounds having the general formula CnH2n'-aAl'a containing unsaturated carbons in the 'molecule in which an aromatic group, (Ar) (or groups, Ara) have been substituted for hydrogen. The aromatic group may be a phenyl group, or a condensed group, such as the naphthalene group, or a polyphenyl group such as the diphenyl group. The term halogenated olefin" is to be understood as limited to those compounds in which the halogen atom is attached to an unsaturated carbon either of the olefin group itself or of an aromatic nucleus.

The liquid halogenated olefins possess also a viscosity which easily, adapts these materials to dielectric purposes, especially in apparatus such as transformers, where low viscosity is demanded for thermal reasons. Trichloror tetrachlorethylene are examples of halogenated liquid olefins suitable for dielectric use. These materials are inert and without corrosive action to metals present in electrical devices. These materialsv have a viscosity of about 30 seconds Saybolt uni- 5o versal and show little change in viscosity over a range oftemperatures. The electrical characteristics of these materials are good. The dielectric strength, tested in a .1" disc electrode gap, gives a valuehigher than 30 kilovolts; The diu from the body of dielectric material It.

electric constant of approximately 8.3 and the power factor of less than 1% at 1000cycles. 25 0., coupled with a characteristic resistivity of about 1: 10 ohms per centimeter cube at 500 volts D. (1., makes these materials particularly welladapted for general dielectric application in and the like.

The transformer shown in Fig. 1 constitutes one example of an electrical device in which a liquid dielectric embodying my invention may be used with advantageous results. As well known, a transformer comprises a tank I containing a magneticcore 2 and electrical windings 3. For the sake of simplicity only a single terminal I, provided with an insulator 5 has been shown, this transformers, circuit breakers, capacitors, cables, I

terminal being connected to one of the windings by a'conductor 6. Mounted onthe cover I, to-

gether with the terminal is condenser 8, provid ed with a jacket 9 through which a cooling fluid may be circulated to condense vapors evolved Inlet and outlet ducts l I, I! are provided for the cooling fluid which conveniently may consist of water. To render the drawing simple and to indicate that its height may be varied the condenser has been shown as broken. It is to be understood that the condenser has been indicated conventionally as representative of any one of various types of condensers either air-cooled or liquid-cooled.

Halogenated olefins have a relatively low boiling point or in other words a high volatility. For

example, dichlor ethylene, CzHzCla, is a liquid which boils at about 55 C,, trichlor ethylene, 021101;, is a liquid which boils at about 87 to 88 0., alpha trichlor propylene, Cal-1:011, is a liquid which boils at about C., and tetrachlor ethylene is a liquid which boils at about C. Vapors evolved from such compounds during the operation of a transformer or other electric device are condensed to the liquid state in the condenser and returned to the mainbody of the cooling medium.

The necessity of using a condenser may be eliminated by the use of a substituted halogenated olefin, the molecule of which contains an aromatic nucleus. Thus although synthetic dichlor ethylene boils at 55 C., the introduction of the benzene nucleus results in dichlor styrolene', or styrene, (CsH5.CC1ZCHCD a product which bolls at 221 C. For many electrical purposes the use of a halogenated olefin containing a substituted aromatic nucleus therefore will be more advanaseousa v Many of the halogenated olefins possess a relatively high congealing point which tends to restrict their use for dielectric purposes. As already indicated, a lower congealing temperature (pour point) may be secured by compounding the halogenated olefin with a halogenated aromatic compound of the type represented by a halogenated benzene, a halogenated po yp ony], such as halogenated diphenyl, or the halogenated derivatives of diphenyl ketone, diphenyl methane, diphenyl benzene, or diphenyl oxide or with halogenated naphthalene, a halogenated compound containing condensed nuclei. For most purposes chlorine compounds are to be preferred over compounds containing bromine or other halogens.

As an illustration of the characteristics of such blended compositions, I cite the case of tetrachlor ethylene compounded or mixed with pentachlor diphenyl as-an example of a chlorinated polyphenyl. In Fig. 2 is indicated the extraordinary and unexpected decrease in pour point of liquid compositions resulting in such case. The pour points or congealing temperatures are plotted here as ordinates and the percentages of halogenated diphenyl as abscissa. In the specific case here taken, the diphenyl compound is. the technical pentachlor diphenyl which itself is a viscous material having a pour point of about +10 C. The pour points were determined by the standard methods adopted by the American So-' ciety for Testing Materials. As pentachlor di- 1 phenyl is present in increasing amounts in the mixture (accompanied by a corresponding decrease of tetrachlor ethylene), the pour point of the mixture drops to a value lower than 50 C. This extremely low pour point is found in a mix- '1 ture made up of equal parts by weight of tetrachlor ethylene and pentachlor diphenyl. As indicated by dotted lines the exactpour point of the 50:50 mixture was not detennined experimentally because of the difllculty of working at such low 1 temperatures. The viscosity of such a mixture is not materially diiferent from the viscosity of the pure tetrachlor ethylene, alone, being 30 seconds Saybolt universal at 37.8 C. Under the same test- 2 ing conditions tetrachlor ethylene has a viscosity of 28 seconds Saybolt. Pentachlor diphenyl has a very high viscosity. At the commonly used testing temperature at 37.8 C. the viscosity of pentachlor diphenyl is 1200 seconds Saybolt unia versal.

Such mixed halogenated products constitute a materialparticularly well adapted for use in apparatus exposed to .low temperature conditions. Other mixtures of chlorinated oleflns and chlor- 3 inated cyclic compounds are characterized by extraordinary low congealing temperatures. The pour point of a mixture of 25% by weight or more of trichlor ethylene and 75% or less of pentachlor diphenyl is lower than 60 C.- The 4 viscosity of the 50:50 mixture is about 34 seconds Saybolt universal.

WhileI have illustrated my invention with particular'reference to chlorine as a particular halogen in products embodying my invention, products containing other halogens are not precluded and such products are to be considered as being included in the present invention.

The term "olefin" is used herein to designate ordinary forms of such compounds as distin- 5| guishedfrom solid resinous olefin polymerization products such as described in Clark and Kutz U. 8. Patent 1,998,309 of March 16, 1935.

Halogenated olefin products in many cases can be advantageously compounded with an oil, either 54 a hydrocarbon oil, for' example, a petroleum oil; or a glyceride oil, for example, castor oil. In some industrial fields, an admixture of a halogenated product, such, for example, as trichlor, or tetrachlor ethylene, renders an oil better suited at for its purposes while at the same time rendering it less inflammable. For most purposes the oil should be in a preponderant proportion by vol.- ume in the mixture. Although I have herein re- 'ferred mainly to dielectric and cooling uses of 5 a,o1o,aaa a 3 portion of which consists of trichlor ethylene and chlorinated diphenyl.

3.'A dielectric composition containing tetrachlor ethylene and a chlor polyphenyl as substantial ingredients.

4. A dielectric composition containing sub stantial amounts of tetrachlor ethylene and pentachlor diphenyl.

5. A composition of matter containing substantial proportions of a halogenated olefin-cornpound containing an aromatic group and a substantial proportion of halogenated cyclic hydrocarbon compound.

6. A composition of matter containing a substantial proportion of halogenated styrolene and a substantial proportion oi halogenated polyphenyl compound. v

7. A composition of matter containing as sub-' stantial ingredients chlor olefin and chlor polyphenyl.

'8, A liquid composition suitable for insulating use in electrical apparatus comprising as substantial ingredients liquid chlor ethylene and 10 chlor polyphenyl. l

FRANK M. CLARK. 

